PROJECT SUMMARY: Alzheimer?s disease (AD) is characterized by a complex pathogenesis for which unifying mechanisms have been actively sought. Among them, autophagy has received a lot of attention, and today there is a general consensus that its dysfunction plays a central role in AD pathogenesis, establishing this cellular system as an ideal therapeutic target. Hence the discovery of pharmacologic tools that can restore autophagy in the brains of AD patients is a highly desirable goal. We have recently discovered that the neuronal 12/15- Lipoxygenase (12/15-LOX) is an endogenous regulator of autophagy since its pharmacologic inhibition or genetic absence result in autophagy activation and clearance of insoluble amyloid beta (A?) and tau. The goal of this research is to develop selective and potent pharmacologic inhibitors of 12/15-LOX and to assess them as novel disease-modifying agents in AD and related tauopathy models. The protein is widely expressed in areas prone to neurodegeneration, such as cortex and hippocampus, and its levels are significantly elevated in patients with AD and mild cognitive impairment, suggesting an early involvement of the pathway in AD pathogenesis. Our laboratories have shown that genetic manipulation of 12/15-LOX modulates cognitive impairment and the development of AD-like neuropathology in mouse models of the disease. In addition, we demonstrated the 12/15-LOX pharmacological blockade by PD146176 activates autophagy and thus rescues learning/memory deficits, facilitates A? and insoluble tau clearance and improves synaptic integrity in aged 3xTg mice. However, PD146176 is off-patent and has poor LOX isozyme selectivity. Therefore, probing more selective and potent 12/15-LOX inhibitors that retain the pro-autophagy activity may ultimately provide a novel therapeutic approach with real disease-modifying capacity for AD. As part of this effort, we recently discovered a novel and highly selective 12/15-LOX inhibitor, ML351, which is brain penetrant and has a good pharmacokinetic profile. In this proposal we will assess ML351 in mouse models of AD and related tauopathies: one that develops A? plaques and tau tangles together with memory impairments (i.e., 3xTg mice); a one that manifests only tau pathology and behavioral deficits (htau mice). At the same time, we will search for additional candidate molecules toward therapeutic development against AD, utilizing our assays to identify novel, selective inhibitors for the human 12/15-LOX. We already have derivatives of ML351, and performed a successful 12/15-LOX high-throughput screen of a new 500,000 compound library and will test the top potent/selective hits for their in vitro and in vivo effectiveness. Considering that ML351 has already been shown to cross the blood-brain barrier and protect against stroke damage, we are confident these studies will demonstrate that ML351, by activating autophagy, protects against the development of the AD-like phenotype and thus has an excellent chance of becoming an effective therapeutic tool to prevent the onset or halt the progression of AD and related tauopathies.